The present invention relates to the field of digital video format conversion. More specifically, the present invention relates to universal format conversion architecture which processes combined video and computer generated imagery.
Today, in the digital television (DTV) post production environment, the use of video and computer generated imagery (CGI) of different formats has become commonplace. Format conversion of high quality, real time video raster CGI is becoming an integral part of the routine operation for efficient DTV content creation and delivery. Most existing video/graphics workstations rely on the CPU and its graphic-subsystem to perform image interpolation in software. When these software systems are used, incoming materials need to be rendered in a suitable format before image editing or composition can take place. A more productive alternative may be to use a dedicated hardware format converter (FC).
Due to the distinct signal characteristics (e.g., the bandwidth) of live video and CGI, however, a format converter optimized for scaling video is not necessarily suitable for CGI. Performance compromises such as image aliasing, ringing and blurring artifacts usually have to be made within a single interpolator design. To overcome the performance barrier constrained by one interpolator, there is a need for a new FC architecture for simultaneous video and CGI scaling.
In the advent of DTV age, the DTV transmission formats specified by ATSC have been adopted by all the major US TV networks. One TV network however, may be in favor of one DTV format while another network may prefer a different one. Multiple DTV formats will continue to complicate video post-production process since video/graphics workstations must be designed to work with multiple input and output formats. Therefore, format conversion is inevitable in DTV post-production and a practical solution must be found. While some high-end video/graphics workstations offer xe2x80x9cresolution independencexe2x80x9d by using software image interpolation, this results in a trade-off between operational speed and system resources allocation for image scaling tasks. To be more productive, a dedicated image-scaling hardware engine that operates efficiently with any mix of DTV-format sources is needed. This is particularly important for post processing companies wishing to serve a broad range of clients who will be working in a variety of standards. In addition, the ability to mix formats allows free use of all program assets, including both traditional video and computer generated imagery (CGI).
The distinctly different signal characteristics of traditional video and CGI are desirably taken into consideration in the design of a format converter. a Conventional wisdom is that all CGIs which have bandwidths that reach the Nyquist limit (ie., 0.5 cycle/pixel) are desirably passed through an anti-aliasing filter before they are scaled just to avoid ringing artifacts. Unnecessary antialiasing filtering for CGI image components, however, may cause image blurring which may diminish the visual appeal of these image components. On the other hand, it is desirable to maintain the bandwidth of CGI image components so that they may be properly displayed on digital display devices such as Plasma Display Panels (PDP) and Digital Light Processing (DLP) video projectors since these devices are capable of displaying CGI to its 0.5 cycle/pixel bandwidth limit. Because digital displays have 100% modulation transfer functions (MTFs), a graphics artist now has an opportunity to show off his artwork in the way that he intended to display it. There is a need for an architecture that can scale any CGI without trading graphics sharpness for other scaling artifacts (such as ringing) reduction.
The present invention provides a simple and effective means for a universal format conversion for use with images containing mixed video and computer generated imagery. A first intermediate scaled image is generated using a first interpolator. The first intermediate scaled image is then processed through an edge extractor to produce a scaled edge image. Next, a second intermediate scaled image is generated using a second interpolator. Then the scaled edge image is added to the second intermediate scaled image to produce a converted image.
In one embodiment a new format conversion architecture is based on dual FCs with the interpolators residing in the two FCs having complementary characteristics.